In the field of computer graphics, the rendering of two-dimensional objects is of fundamental importance. Two-dimensional objects, such as character shapes, corporate logos, and elements of an illustration contained in a document, are rendered as static images or as a sequence of frames comprising an animation. There are numerous representations for two-dimensional objects and it is often the case that one representation is better than another representation for specific operations such as rendering and editing. In these cases, a conversion from one form to another is performed.
Distance fields have proven to be an effective representation for rendering and editing two-dimensional shapes, as demonstrated by the following patents, all incorporated herein by reference: U.S. Pat. No. 6,396,492, issued May 28, 2002, entitled “Detail-directed hierarchical distance fields;” U.S. Pat. No. 7,034,845, issued Mar. 13, 2007, entitled “Antialiasing an Object Represented as a Two-Dimensional Distance Field in Image-Order;” U.S. Pat. No. 7,123,271, issued Oct. 17, 2006, entitled “Antialiasing a Set of Objects Represented as a Set of 2D Distance Fields in Image-Order;” and U.S. Pat. No. 6,917,369, issued Jul. 12, 2005, entitled “Method and Apparatus for Rendering Cell-based Distance Fields using Texture Mapping.”
Although we focus here on digital type, possibly the most common and important two-dimensional object, the following discussion applies to all types of two-dimensional objects.
We begin with some basic background on digital type. A typical Latin font family, such as Times New Roman or Arial, includes a set of fonts, e.g., regular, italic, bold, and bold italic. Each font includes a set of individual character shapes called glyphs. Each glyph is distinguished by its various design features, such as underlying geometry, stroke thickness, serifs, joinery, placement and number of contours, and ratio of thin-to-thick strokes.
There are a number of ways to represent fonts, including outlines, uniform width strokes, and stylized strokes.
Outline-based representations have been adopted and popularized by Bitstream Inc. of Cambridge, Mass., Adobe Systems, Inc. of Mountain View, Calif., Apple Computer, Inc., of Cupertino, Calif., Microsoft Corporation of Bellevue, Wash., URW of Hamburg, Germany, and Agfa Compugraphic of Wilmington, Mass.
To optimize memory usage, uniform width stroke fonts can be used. These fonts typically group sets of uniform width strokes, a.k.a. radicals or graphemes, which are commonly repeated in Chinese characters throughout a font, as a single simple shape that is then reused across characters.
Stylized Stroke Fonts (SSFs) are enhanced stroke-based fonts whose strokes have variable thickness and stylistic stroke ends, see “An Improved Representation for Stroke-based Fonts”, SIGGRAPH 2006 Conference Abstracts and Applications, Elena J. Jakubiak, Ronald N. Perry, and Sarah F. Frisken.
SSFs are also described in U.S. Non-Provisional patent application Ser. No. 12/359,819 “Method for Converting Outline Characters to Stylized Stroke Characters,” filed by Jakubiak et al. on Jan. 26, 2009, incorporated herein by reference.
SSFs employ a modular structure that leverages the repetition of shape within a font, enabling SSFs to match the expressiveness of outline fonts with a memory footprint comparable to current uniform width stroke fonts.
To enable the use of distance-based rendering, see, for example, U.S. Pat. No. 6,917,369 “Method and Apparatus for Rendering Cell-based Distance Fields using Texture Mapping,” incorporated herein by reference, as well as other operations such as editing, space and time efficient methods are required for generating a distance field of an object, such as a glyph, represented by various forms.
It is an object of the invention to provide a space and time efficient method for generating a distance field of an object represented by outlines.